Blood consists of a number of components having different characteristics and uses. Advances in understanding these characteristics and uses have resulted in increased utilization of the specific fractions of blood, rather than whole blood, for therapeutic purposes. In view of the substantial therapeutic and monetary value of blood components, a variety of techniques have been developed to separate blood into its component fractions while ensuring maximum purity and recovery of each of the components.
The separation of a single unit of donated whole blood (generally about 450-500 milliliters in U.S. practice) into its components is typically accomplished by use of differential sedimentation. Typically, the principal components thus recovered are red cells, usually concentrated as packed red cells (PRC), platelet concentrate (PC), and plasma. The plasma may be further processed to yield a variety of valuable products.
There are two principal methods for separation of whole blood into components by differential sedimentation. In the most common method, the whole blood is typically centrifuged at a slow speed to produce a supernatant PRP fraction and a sediment PRC fraction, with a transition zone material in between, generally known as the buffy coat, which contains white blood cells (known collectively as leukocytes), as well as platelets, red cells, and plasma. The PRP fraction is separated from the buffy coat and PRC and then further processed by high speed centrifugation to produce a supernatant plasma fraction and a sediment platelet-containing fraction. The two fractions are then separated, and the platelet-containing fraction is processed to form PC.
In an alternative method, the whole blood may be centrifuged at a high speed to produce a supernatant platelet-poor plasma (PPP) fraction, and a sediment PRC fraction, with a transition zone material, the buffy coat, therebetween, which contains the majority of platelets, as well as leukocytes, red cells, and plasma. The buffy coat is separated from the supernatant PPP and the sediment PRC and then further processed by low speed centrifugation to form a supernatant platelet-containing fraction, and a sediment red cell containing fraction. The supernatant platelet-containing fraction is then separated from the sediment fraction, and processed to form PC.
However, despite the differences between the common and alternative methods, both techniques share several drawbacks, including the potential for red cell contamination and leukocyte contamination. With respect to red cell contamination, the presence of red cells in some blood components (e.g., PC) is so undesirable that the technician operating the blood processing equipment typically constantly monitors the process to ensure that red cells will be excluded. For example, regardless of whether the operator is separating PRP from PRC, or separating the buffy coat from the sediment PRC and/or separating the supernatant platelet-containing solution, the operator must closely monitor the separation and clamp the connecting tube between the blood bags when, in his judgment, as much fluid has been transferred as is possible, consistent with allowing no red cells to pass. This is a time consuming operation during which the operator must visually monitor the bag and judiciously ascertain when to shut-off the connecting tube.
The problem of red cell contamination presents an additional dilemma. Since platelets and plasma are valuable blood components, blood bank personnel may attempt to express more of the PRP or the supernatant platelet-containing fraction prior to stopping the flow from the blood bag. This is counterproductive in that the expressed fluid may be contaminated by red cells. The presence of red cells in PC is so highly undesirable that the PC may be discarded or subjected to recentrifugation, both of which increase operating costs and are labor intensive. As a result, blood bank personnel may err on the side of caution by prematurely stopping the flow of the platelet-containing fluid, e.g., PRP and/or supernatant platelet-containing fraction, before it has been fully expressed.
With respect to leukocyte contamination, both methods may produce leukocyte-containing fractions. It is now generally accepted that it is highly desirable to reduce the leukocyte concentration of each of the blood components by at least 70%, since the presence of leukocytes may adversely affect the storage life of the fractions, and/or cause undesirable effects when the fractions are transfused into a patient.
These problems may lead to reduced yields of valuable blood components since it may be difficult to eliminate red cell and leukocyte contamination while maximizing the yield of the various valuable blood components. For example, while the transition zone material or the buffy coat contains valuable platelets, plasma, and red blood cells, it may also contain a considerable amount of undesirable leukocytes. Since it may be difficult to easily or efficiently separate the various valuable components from each other, as well as from the leukocytes, the buffy coat may be partially or entirely discarded, resulting in reduced yields of valuable blood components such as plasma and platelets.
The loss of platelets is especially significant, since the lost platelets may include the most desirable platelets, i.e., the newly formed platelets. Newly formed platelets are larger and are generally believed to be more active. Since the younger platelets are larger, they tend to sediment faster during centrifugation, so these platelets may be concentrated as in one of the embodiments described below in the bottom of the PRP and in the buffy coat. Accordingly, since portions of these fractions or zone may be either processed as part of the PRC, or discarded, this represents a significant loss of the more desirable platelets.
For example, with respect to the conventional method of processing whole blood to form PRP and PRC, the buffy coat may be discarded after expression of the PRP and PRC layers, or, since the buffy coat may remain in the collection bag along with the PRC after the PRP fraction has been expressed, the buffy coat may be processed with the PRC.
Similarly, with respect to the alternative method of processing whole blood to form a buffy coat between PPP and PRC layers, and then processing the buffy coat to form a supernatant platelet-containing fraction and a sediment red cell containing fraction, the lower portion of the buffy coat may be processed with the PRC. For example, when the buffy coat is expressed before the PRC, the buffy coat may be incompletely expressed to prevent red cell contamination, and the lower portion of the buffy coat may be expressed with the PRC. Alternatively, when the PRC is expressed before the buffy coat, the lower portion of the buffy coat may be expressed along with the PRC.
Furthermore, in separating the supernatant platelet-containing fraction from the sediment red cell containing fraction, the lower portion of the supernatant platelet-containing fraction may be incompletely expressed to avoid red cell contamination, which may decrease the yield of the platelets.
Additionally, conventional methods for the processing of blood to provide blood components may lead to the presence of air, in particular oxygen, in the blood components or in the storage container. This may lead to an impairment of the quality of the blood components and may decrease their storage life. More particularly, oxygen may be associated with an increased metabolic rate (during glycolysis), which may lead to decreased storage life, and decreased viability of the blood components. Furthermore, the presence of air or gas in the satellite bag may present a risk factor to a patient's being transfused with a blood component. For example, as little as 5 ml may cause severe injury or death.
Accordingly, the previously described methods reflect a generally unsatisfying compromise between the pressing need to maximize the yield of the historically valuable blood components such as PC, plasma, and red cells from whole blood samples, and remove gas, while minimizing the effort and expense involved.
All of these problems are magnified when increased volumes (e.g., multiple units) of blood components are pooled or processed. Regardless of the particular method used to process blood into components, when multiple units of blood components are pooled before further processing, some of the fluid is trapped or retained in the individual collection and processing assemblies. Collectively, this represents a significant loss if the highly valuable fluid can not be recovered.
In view of this there is a growing need for a method and system for alleviating the above-described problems while providing maximum purity and a higher yield of superior quality blood components. In particular, there is a pressing need for a system and method for recovery and treatment of the transition zone material or the buffy coat which provides for a maximum yield and minimizes the presence of gas while delivering a greater proportion of viable and physiologically active platelets, e.g., by delivering a higher proportion of younger platelets.
There is also a pressing need for a method and system for efficiently pooling blood components, such as the transition zone material or the buffy coat, that maximizes the amount of fluid that can be recovered, while minimizing the presence of air.
Moreover, there is also a need for a method and system that is easily performed and provides for the separation of gas from the recovered fluid.